How to mock Dio.interceptors.add when write unit test?

[devnta]

Package

dio

Version

5.4.0

Operating-System

Android, iOS

Output of flutter doctor -v

No response

Dart Version

No response

Steps to Reproduce

Sorry for my English.

My real data source class:

class MovieRemoteDataSourceImpl implements MovieDataSource {
  final Dio dio;

  MovieRemoteDataSourceImpl(this.dio);

  @override
  Future<Either<Exception, List<MovieResponse>>> fetchMovies() async {
    const url = Endpoint.getTopRatedMovies;
    try {
      final addHeaderInterceptor = AddHeaderInterceptor();
      dio.interceptors.add(addHeaderInterceptor); // Error in this line when run unit test.
      final response = await dio.get(url);
      final mapFromJson = response.data['results'] as List;
      final result = mapFromJson.map((e) {
        return MovieResponse.fromJson(e);
      }).toList();
      return Right(result);
    } on Exception catch (e) {
      return Left(e);
    }
  }
}

My unit test class:

@GenerateNiceMocks([MockSpec<Dio>()])
void main() {
group('Fetch list of movie.', () {
  MockDio mockDioClient = MockDio();
  final dataSource = MovieRemoteDataSourceImpl(mockDioClient);
  RequestOptions requestOptions = RequestOptions();
  Response mockResponseSuccess = Response(
    requestOptions: requestOptions,
    statusCode: 200,
    data: listOfMovieMock,
  );
  test('Fetch success', () async {
    when(mockDioClient.get(any)).thenAnswer((_) async => mockResponseSuccess);
    final actual = await dataSource.fetchMovies();
    expect(actual.isRight(), true);
  });

  test('Fetch error: 404 Not found', () async {
    when(mockDioClient.get(any)).thenAnswer(
      (_) async => throw DioException(requestOptions: requestOptions),
    );
    final actual = await dataSource.fetchMovies();
    expect(actual.isLeft(), true);
  });
});
}

Then I get an error:

FakeUsedError: 'interceptors'
No stub was found which matches the argument of this method call:
interceptors

A fake object was created for this call, in the hope that it won't be ever accessed.
Here is the stack trace where 'interceptors' was called:
...
However, member 'add' of the created fake object was accessed.
Add a stub for MockDio.interceptors using Mockito's 'when' API.

Expected Result

My unit test is passed.

Actual Result

Occur an error.

[devnta]

For everyone facing the same issue, just add:

final fakeInterceptors = Interceptors();
when(mockDioClient.interceptors).thenReturn(fakeInterceptors);